As is well known, shafts rotating at or near their critical speeds give rise to considerable radial stresses which must be absorbed by their bearings. This is particularly true when the tool carried by the shaft is cantilevered thereon without counterbearing, as is the case with the devices referred to above. Various proposals have been made for reducing these radial stresses, generally through the use of elastic inserts. Thus, it has been proposed to interpose spacers of synthetic rubber between the outer race of a journal bearing and the stationary housing in which that bearing is held. Such a mounting, while mitigating the effects of vibrations due to the radial stresses, does not eliminate their causes, namely the noncoincidence of the axis of rotation with the inertial axis of the rotary body constituted by the tool and its shaft.
German published application No. 1,966,463 discloses acoustic dampers interposed between a high-speed rotor and its ball bearings. According to that publication, the acoustic dampers are several elastic O-rings with a Shore hardness of about 90 which are to be stiff enough to hold the rotor in its substantially centered position. With such a mounting, too, there occurs only a minor reduction of the stresses due to eccentricity.